It's a world where guys have superpowers and the girls are very often disempowered. But now two Glasgow-based women are attempting to shake up the often misogynistic comic book environment with the UK's biggest comic convention, Kapow!, in London this weekend. Sisters Lucy and Sarah Unwin not only hope that their show will be a Glastonbury for geeks but that they will change perceptions that comic conventions are just for the boys.

Now in its second year, the event aims to create an atmosphere that welcomes everyone. The Unwins estimate that 30% of the 10,000-strong audience last year were female and they hope that if the convention is a continued success, more women will want to attend. "I've been to shows in America that definitely have a locker-room feel and ours doesn't. We very carefully try to make our environment more inclusive and friendly," says Lucy Unwin,who refers to the Con Anti-Harassment Project, which aims to tackle sexist behaviour at all conventions.

Unwin is the partner of Mark Millar, arguably Britain's biggest comic book writer and co-creator of Kick-Ass, which became a hit film in 2010 (with a script co-written by Jane Goldman, now one of the UK's biggest screenwriters). Unwin, who has a background in film marketing, admits the comic book scene was something she knew nothing about until she met Millar and that she could not have created Kapow! without his contacts. Having attended enormous US comic conventions such as San Diego's Comic-Con she recognised the market was there. Jonathan Ross, husband of Goldman and self-declared comic geek, will host a superhero v supervillain wrestling match.

But there are only nine female guest speakers out of a guest list of 57 comic creators. "We ourselves as women organising the show have been accused of misogyny because of the obviously male guest list, but there is just this lack of female creators and it's the nature of the industry. There's no point in taking it to heart because I don't employ the creators. I would love there to be more women at the show in terms of guests."

Holding her six-month-old baby Matilda in her lap as she speaks, Lucy talks about the snide remarks and internet trolling she has experienced – almost all of it suggesting that she's just a front for Millar. She says: "It's not very pleasant but I just ignore it. I don't have such a huge ego, I do know it's my show."

Millar is less sanguine and springs to the sisters' defence. "This is their money, their risk and their show and what two sisters have done is come into what was always very much a boys' world and changed the whole game."

Millar, who has been reading comics since he was 14, estimates that just 5% of comic book creators are women and that 10-20% are readers. "There has been a huge influx of female readers since they started the tie-in movies, and comics have changed over the past 10 years. This will mean more female creators as time passes and we are starting to see some big female stars breaking through into what's been a boys' club."

Unwin believes that the male/female landscape of comics is set to change. She says: "We do portfolio reviews at Kapow! and everyone can hand in their artwork and it will be looked at by DC, Marvel and Image. There's a potential for a commission. The hope is that women will feel equally able to hand in stuff. Who knows, maybe we will find the next great female creator this weekend."